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Need a reminder.. yz125

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Hi I need a reminder. I bought a used cylinder with a steel sleeve bored out 2mm over and a piston of the right size. I have powervalves out of a stock bore that I am going to use. Do they have to br grinded down to keep out of way from hitting the piston ??

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Yes you will need to check the valve clearance.

With the cylinder off the bike and on the bench and the valve installed in place...........put a straight edge along the inside cylinder wall and push the valve in and see if it makes contact with the straigh edge. A 150mm steel rule is a good straight edge. Give the valve a little clearance of .5 mm in a cold ambient enviroment if requirement. Now is also the time to check the sleeve for out of round and out of taper. Put a nice cross hatch on the cylinder wall with a ball hone. Don;t forget to check the piston end ring gap and also the piston to cylinder clearance. I like to use 1 thou per inch of bore size and relieve the exhaust bridge if it has one.

 

Kind regards  

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I put the valves in it and while cylinder on the bench I took the piston with the ring on it and pushed it up into it from the bottom really slow whike watching and they do stick out to far the grab the top if the piston a little bit . Didnt even get far enough to grab the ring. No harm done by using my piston. Now do I have to grind the valves down ever so slightly when I take thdm back out . Thats all I can yhienk of and thought I had read that somewhere in the past. And I used a flex hone and got the cross hatching in it too by the way and piston to cylinder clearance is also good.

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I guess this brings me to a new question when grinding the valves down do I grind yhe angled part down or do I just hit the very end of the edge back ?? Im gonna look around online some but having a hard time finding the info

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You can do it a few ways and I like to use a die grinder with a blue stone. Not a steel die grinding bit as it will take too much material off at once. The ideal way is to keep the rake and angle but you can grind the edge and then put a matching chamfer on the end to match the angles. If you have to grind in 1 mm or so then match the angle. The idea is to point the edge a little, not too much like a knife edge, to match where it lays back into the cylinder exhaust port and also for flow. If you are unfamiliar with small pencil die grinders then check out Ken O'Connor racing on you tube to get an idea. I also like to sand back and polish the valves but it all depends on what your preference is.

Good luck. Do some Google investigation but I would allow 0.5mm clearance if possible. 

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Ok I did what you said I used a vice to hold the valves a dril and bit I used a but aggressive but I reinstalled them every so often to make sure theyed be even and so I didnt take off too much slid tge piston and ring in by hand got it to my likings and then I sanded them down smooth. Installed the piston and cylinder gitbthe bike back together its running pretty well in the break in process now. Its an 01 yz 125 got it for 600 and got about 300 in it now. So im satisfied with it as long as it stays running as long is one normaly would. Now I need to rebuild the shock before any motocross :/ but oh well its running. Back to work on my other bike now..04 kx250f

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